OK, it's almost a passive house, so needs very little in the way of heating. It's heavily insulated all the way round, in the case of the walls the construction is part of the insulation (40mm fibreboard externally, then 140mm I beam filled with warmcel, then 18mm OSB). The whole thing is extremely airtight, airflow is controlled via a whole house MVHR system. We have a small gas boiler running a very low temp underfloor heating system (cuts out at screed temp of 27C) and in one room (the posh one for mums and dads) we've got the lowest rated woodburner we could find (old parents like a visible heat source).
Very nice, congrats! But I do wonder a few things. I'm very interested in passive houses and that's why I also tried to build as passive as possible when we built out house, now 3 years ago. We didn't quite reach the passive norm, just the 'very low energy' norm.
1) Were bricks used for the supporting structure, or was it a wooden skeleton?
2) I'm sorry, but to me the amount of insulation doesn't seem all that much, not for passive standards anyway. 140 mm with warmcell is only about half to one third of what is needed for the house to be truely passive. The few months in which you claim only to need heating also seem very optimistic to me. In my case: we used 100 mm polyurethane which has a better lambda value than warmcell (so it insulates better per mm) The R value (larger is better) of our insulation is (thickness in meters / lambda value) 0.1/0.023= 4.34mēK/W. The lambda value of warmcell is 0.035 (best value) to 0.040 (worst value). In this example I'll use the best value. So your R value is 0.14/0.035= 4mēK/W. Conclusion: our house is still insulated a tad better with our 100 mm of polyurethane than yours is with your 140mm of warmcell. For the k value, you need to do 1/R, so for my insulation that's 0.23W/mēK and for your insulation that's 0.25W/mēK. (smaller is better here) Of course, to be completely correct, you need to add all the materials in the entire wall. In your case this means I would have to add the k values of the 40mm fibreboard and the 18mm OSB and most likely 15 mm of plaster on the inside as well.
In any case, our houses are insulated about the same, and they are built in areas with similar environmental conditions. Still, we could never go without additional heating from October to April/May. Granted, we use a low kW heat pump, but there's no way we could do without. I simply cannot imagine you needs so much less heating... maybe it is different for you if you haven't used bricks but used all wood? (just guessing here?), or maybe you can tolerate cold better than I can, but still... ?
3) Did you use triple-layer glass for the windows? Maybe even the so-called 4-season glass which has a special filter, which decrease your g-factor a lot?
4) I really can't get my head around the building style. Don't get me wrong, I like the look personally, but it seems very inefficient for a passive house. For passive, best is to have a boring square or rectangular house with a normal roof (a 'compact' house). I find the shape of your house, with all the sections like the garage and the living room jumping 'out' (I don't know really how to put this, I hope you'll know what I mean) like they do really inefficient because they all are extra surface that is in contact with the air outside the house. All this extra surface inevitably means more loss of heat through the walls and roof. Naturally it's imperitive this should be avoided at all cost in a passive house. Flat roofs can be done, but also are more difficult to insulate. I can see you did the homework on your windows though ; small to no windows on the North side, most other windows in the South side of the house. Were this factors you took into account, but let the look of the house be decicive in the end? (I could understand that)
5) Did you do a
blower door test to test the airtightness of the house? If so, what was your g (small g) value? (just for my curiosity
) Did you have a thermal image scan of your house done?
6) For ventilation, you say you use a MVHR system. What unit did you use? Is the inlet simply pulled air from outside, or does the air get pre-treated via the heat in the soil outside the house? (I don't know the correct name of these devices in English, but literally translated they should be called "Soil Heat Exchanger" or something like that)
7) What is the kW value of your gas boiler? I suppose you also heat your hot tap water with this gas boiler? Or did you install a solar boiler? (can't really tell from the photos, but I think not?)
8) Did you install photovoltaic panels?
I hope all my questions don't overwhealm you, but for me this is very facinating stuff.
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